The present invention relates to a method and an apparatus for filling a flexible package, in particular a bag, with loose materials and in particular with bulk goods, wherein the flexible package is filled by means of a filling element. The invention serves to bag powdered or granular products and in particular to bag lightweight and very fine, powdered products such as aerosils, and carbon black particles employed in paint manufacture or TiO2 particles or TiO2-containing materials or the like where the bulk goods contain a considerable amount of air during filling. The invention is furthermore suitable for bagging other kinds of loose or free-flowing bulk materials or for bagging toxic or environmentally hazardous products.
Different systems for bagging bulk materials have become known in the prior art. In conventional systems for filling loose bulk goods into valved bags, the bulk goods include a certain air content during filling. The air content in the bag is allowed to gradually escape to the exterior through corresponding vents in the bag wall.
Still, excess pressure will exist in the bag during the filling process, for example approximately 150 to 250 millibars. Such excess pressure is still present as the filling element is cut off. Now when the bag is pulled off the filling element at the moment of cutting off, the pressure in the bag will be abruptly released through the valve, which is still open, so as to release to the exterior of the bag a certain quantity of material which in particular in the case of lightweight materials can be substantial. This will cause loss of bag weight and also contamination of the system and the bags. When bagging for example carbon black particles or TiO2 particles, small quantities of escaped goods will already cause quite considerable contamination in the environment.
To reduce material escape and to improve the cleanliness of the installation and the bags, the prior art therefore provides that discharge of the bag is deferred until the pressure in the bag interior has dropped, or else the excess pressure needs to be released through a bypass. Pressure decrease through the walls in particular in the case of lightweight materials is very time-consuming such that a dramatic reduction of the bagging capacity must be expected. While releasing the pressure through a bypass accelerates the pressure decrease, material is not prevented from also escaping through the bypass which then results in weight loss of the bags. This may lead to substantial weight fluctuations. Also, escaped material must as a rule be discarded. On the whole, this condition will increase operating costs.
In the prior art, U.S. Pat. No. 3,533,454 has disclosed an apparatus for filling material into bags. During the filling operation the side faces of the bag are initially crushed in. During filling the side walls are then allowed to expand such that the filling material will not seal the pores in the side walls of the bag during the filling operation. The open pores are intended to provide continuous venting during filling. Such continuous venting may increase the filling rate in operation. This known method will only relatively slightly reduce the entire filling process because it is significantly determined by the maximum pressure in the bag at the end of filling and the subsequent waiting time after filling is terminated. Since the maximum pressure remains unchanged, the time required for the pressure decrease and thus the waiting time also remain unchanged.
In the prior art there was further disclosed in DE 195 41 975 A1, a method and an apparatus for forming and venting open bags after filling wherein the top edges of the bag wall overhangs are slidingly clamped in jaws and wherein after filling the clamping jaws are rolled in the direction of the bag filling level so as to allow the retained air to escape from the bag by means of a lance inserted in the bag through the upper feed inlet on which a vacuum can be applied. In this way the waiting time can be effectively reduced. One disadvantage of the known apparatus is, however, that the lance introduced into the bag does not only allow air but also filled material to escape.
DE 37 03 714 A1 discloses a bagging machine for bagging powdered goods by way of a filling spout which filling spout is provided with an air outlet equipped with a filter and connected with a vacuum source to draw the air out of the bag by suction. This apparatus may be used for filling powdered materials into valved bags. It is a disadvantage of the known apparatus, however, that when employing a coarse-pored filter, considerable quantities of filling material still escape through the outlet while when employing a fine-pored filter, the pores clog up rapidly and thus considerably reduce effectiveness.
These apparatus known from the prior art must thus, wherever material can escape from the bag with the air, provide for the bags to be overfilled by the expected amount of weight loss to reduce or compensate for weight fluctuations of the filled bags. Since such weight losses vary, weights will inevitably be largely scattered such that, in order to comply with minimum weights, more material must as a rule be bagged than is in fact required. Alternatively the settling time after the end of the filling operation may be extended for the excess pressure to drop.
In all of the cases described there is a disadvantage to the method by way of a noticeable cost increase, by clearly reduced capacities, and/or by loss of material and possibly contaminated bags.
There is furthermore described in the unpublished international patent application PCT/EP2007/010252, an apparatus and a method for filling bags with loose goods, wherein a package to be filled is filled through a filling element by means of a filling process. The filling process comprises a filling stage, a settling stage, and a discharge stage. During the filling stage, loose material is filled into the package; in the settling stage, a settling phase is provided for the pressure to decrease; and in the discharge stage, the package is discharged from the filling element. The filling process is shortened in that the volume available to the package during a considerable portion of the filling process, is reduced so as to maintain a high pressure inside the package, while at the end of the filling process, the available volume of the package is expanded to rapidly reduce the pressure prevailing in the package.
In view of the prior published state of the art it is the object of the present invention to provide a method and an apparatus which allow a rapid filling of flexible packages while at discharge there will be only slight or even virtually no loss of weight.
This object is solved by a method having the features of claim 1. The apparatus according to the invention is the object of claim 17. Preferred specific embodiments of the invention are the subjects of the subclaims. Further advantages and characteristics can be taken from the embodiment.